Fig. 4. New outflow tract myocardium is derived from splanchnic mesoderm caudal and
adjacent to the outflow. (A) Diagram of a stage 14 chick embryo showing the
location of the secondary cardiac outflow field (yellow asterisk), which is
located at this stage adjacent to the second arch (green). (B) Confocal image
of a stage 22 chick embryo injected into the secondary heart field just caudal
to the outflow tract with mitotracker at stage 14. Two new segments, a
proximal fluorescent segment (asterisk) and a more distal non-fluorescent
segment (star), were added to the primary tube between the time of injection
at stage 14 and acquisition of this image at stage 22. The fluorescent spot
(white arrow) cranial to the outflow tract shows the needle entry site for the
mitotracker injection, which was originally posterior to the outflow tract.
(C) The secondary heart forming region was removed from a stage 14 quail
embryo and placed in the comparable site of a chick embryo at a similar stage.
A transverse section at the level of the distal outflow myocardium shows two
small vesicles with quail cells (QCPN antibody, brown) adjacent to the outflow
tract (arrow). (D) Higher magnification of the vesicles reveals an inner lumen
lined with quail cell epithelium, surrounded by MF20-positive (purple)
myocardial cells. Scale bars: 100 µm.
